GLUCONO DELTA-LACTONE
EXPLANATION
Glucono delta-lactone (GDL) was evaluated for acceptable daily
intake at the tenth and eighteenth meetings of the Joint FAO/WHO
Expert Committee on Food Additives (Annex 1, references 13 and 35).
Toxicological monographs were published after both of these meetings
(Annex 1, references 12 and 36).
Since the previous evaluation, at which time an ADI of 0-50 mg/kg
b.w. was established, additional data have become available and are
summarized and discussed in the following monograph. The previously-
published monograph has been expanded and is reproduced in its
entirety below.
BIOLOGICAL DATA
Biochemical aspects
GDL, in an aqueous medium, readily forms an equilibrium mixture
of the lactone and gluconic acid. These are intermediates in the
oxidation of glucose through the pentose phosphate cycle, which, while
not the main pathway of glucose metabolism, is well recognized.
GDL was reported to inhibit competitively mannosidase and
glucosidase isolated from rat epididymis and limpet tissue
(Levvy et al., 1964). These findings were confirmed using acid
alpha-glucosidase from rabbits (Palmer, 1971).
GDL is a non-competitive inhibitor of polysaccharide
phosphorylase in in vitro assays (Tu et al., 1971).
The enzyme gluconolactonase (E.C. 3.1.1.17) has been isolated
from porcine liver; it was found to catalyze the hydrolysis of GDL to
gluconic acid with maximum activity at pH 7.5 (Roberts et al.,
1978).
Groups of six rats were fed a diet in which the limiting factor
was inadequate caloric value. When the basal diet was supplemented
with either glucose or GDL, as a source of additional calories,
increased growth rate was observed. Glucose and GDL were almost
equally effective in the promotion of growth (Eyles & Lewis, 1943).
Sodium gluconate uniformly labelled with 14C and 2H was
administered i.p. to normal rats for three successive days.
Approximately 57% of the administered 14C label appeared in expired
CO2. Only a small fraction of gluconate carbon could be recovered as
urinary saccharate. When labelled gluconate was administered to
phlorizinized rats, about 10% of the total 14C label appeared in the
expired CO2. Urinary glucose from phlorizinized rats and liver
glycogen from normal rats were shown to be uniformly labelled with
respect to 14C (Stetten & Stetten, 1950).
Radioactivity was measured in the blood of normal and
alloxan-diabetic Wistar rats after the oral administration of
(U-14C)-GDL or (U-14C)-gluconate. Radioactivity was also measured
in the intestinal contents and faeces 5 hours after ingestion of the
radioactive materials. The authors concluded that the lactone is
better-absorbed from the intestine than is the gluconate anion.
Because of enhanced membrane permeation and higher concentrations of
the lactone in blood, the distribution space of the lactone is larger
than that of gluconate (50 and 41% of the body weight, respectively);
a higher retention in tissues and a greater loss in urine was also
observed after administration of the lactone. Incorporation into liver
glycogen was higher after the administration of the lactone than after
the administration of gluconate, particularly in diabetic animals. The
initial deficit in the oxidation of gluconate compared to that of the
lactone, caused by a lag period of 7 and 4 hours, respectively, was
completely compensated for during the following 8-9 hours. The
oxidative turnover of both compounds was significantly enhanced in
diabetic animals. The better utilization in diabetic metabolism is in
part explained by a rise of glycolytic intermediates in the liver,
which are decreased in starvation and diabetes. Initial
phosphorylation is the limiting step of gluconate metabolism
(Tharandt et al., 1979.
When three men were given 10 g (167 mg/kg b.w.) of GDL orally as
a 10% solution, the amounts recovered in the urine in 7 hours
represented 7.7-15% of the dose. No pathological urine constituents
were noted. When 5 g (84 mg/kg b.w.) was given orally, none was
recovered in the urine. The largest dose given was 30 g (500 mg/kg
b.w.) (Chenoweth et al., 1941).
Toxicological studies
Special study on mutagenicity
The mutagenic effects of GDL were assessed in Saccharomycescerevisiae and Salmonella typhimurium strains TA1535 and TA1537,
with and without metabolic actuation. GDL was not mutagenic in these
assays at doses of 0.25 and 0.5% (Litton Bionetics, Inc., 1974).
Special studies on teratogenicity
Mice
Six groups of 25 pregnant mice were given continuously from days
6-15 of gestation 0, 6.95, 32.5, 150, or 695 mg/kg b.w./day GDL by
oral intubation. A positive control group that was administered
150 mg/kg b.w./day aspirin was included. No clearly-discernible
effects were seen on nidation or on maternal or fetal survival. The
number of abnormalities seen in either soft or skeletal tissues of
animals in the test groups did not differ from the number occurring
spontaneously in the sham-treated controls (FDRL, 1974).
Rats
Six groups of 22 to 25 pregnant rats were given continuously from
days 6-15 of gestation 0, 5.94, 27.6, 128, or 594 mg/kg b.w./day GDL
by oral intubation. A positive control group that was administered
250 mg/kg b.w./day aspirin was included. No clearly-discernible
effects were seen on nidation or on maternal or fetal survival. The
number of abnormalities seen in either soft or skeletal tissues of
animals in the test groups did not differ from the number occurring
spontaneously in the sham-treated controls (FDRL, 1974).
Hamsters
Six groups of approximately 25 pregnant hamsters were given
continuously from days 6-10 of gestation 0, 5.6, 26, 121, or 560 mg/kg
b.w./day GDL by oral intubation. A positive control group that was
administered 250 mg/kg b.w./day aspirin was included. No
clearly-discernible effects were seen on nidation or on maternal or
fetal survival. The number of abnormalities seen in either soft or
skeletal tissues of animals in the test groups did not differ from the
number occurring spontaneously in the sham-treated controls
(FDRL, 1974).
Rabbits
Six groups of 10 pregnant rabbits were given continuously from
days 6-18 of gestation 0, 7.8, 32.2, 168, or 780 mg/kg b.w./day GDL by
oral intubation. A positive control group that was administered
2.5 mg/kg b.w./day 6-aminonicotinamide was included. No clearly-
discernible effects were seen on nidation or on maternal or fetal
survival. The number of abnormalities seen in either soft or skeletal
tissues of animals in the test groups did not differ from the number
occurring spontaneously in the sham-treated controls (FDRL, 1974).
Acute toxicity
LD50
Species Compound Route (mg/kg b.w.) Reference
Rabbit Sodium gluconate i.v. 7630 Gajatto, 1939
Short-term studies
Rats
Groups of 20 male and 20 female rats were fed gluconic acid
(as GDL) for 26 weeks at levels of 0 or 1% in the diet without
ill-effects or demonstrable changes in the main organs on microscopic
examination (Harper & Gaunt, 1962).
Cats and dogs
Gluconic acid was administered as a 10% solution by stomach tube
to 5 cats and 3 dogs at a daily dose of 1.0 g/kg b.w. for 14 days.
Urine was examined daily for protein, blood, casts, and sugar. Gross
examination of lungs, heart, liver, kidneys, gastrointestinal tract,
bladder, ureters, and spleen as well as histological examination of
lungs, liver, and kidneys were performed. No evidence of toxicity was
found. (Chenoweth et al., 1941).
Long-term study
Rats
Groups of 30 male and 30 female rats were fed diets containing
meat treated with 1% GDL (equivalent to feeding 0.4% GDL) or untreated
meat for 29 months. Growth, food intake, and mortality were not
affected. Haematology, clinical biochemistry, liver function tests,
and histopathology revealed no differences between treated animals and
controls (Van Logten et al., 1972).
Observations in man
Sixteen persons (7 with urologic conditions) were administered
5-g doses of GDL at 2-hour intervals, up to total doses of 15 to 25 g
daily, and subsequently 10-g doses, up to total doses of 20 to 50 g
daily. The pH and specific gravity of the urine from those on test and
from the controls were determined. In g of the 16 patients, the urine
became more acid, and in the other half it became more alkaline during
the period of treatment. Eleven of the 16 patients developed diarrhoea
without nausea during the course of the study (Gold & Civin, 1939).
The administration for 3 to 6 days of large oral doses
(5-10 g/day) of gluconic acid to five normal humans did not produce
any renal changes, as shown by the absence of blood, protein, casts,
or sugar in the urine (Chenoweth et al., 1941).
Comments
GDL, in an aqueous medium, readily forms an equilibrium mixture
of the lactone and gluconic acid. these are intermediates in the
oxidation of glucose through the pentose phosphate cycle.
A single long-term test in rats with 1 level of GDL in the diet
showed no evidence of carcinogenicity. Teratogenicity studies have
shown no abnormalities in several species. GDL was not mutagenic in
microbial tests.
GDL makes an insignificant contribution to the normal
carbohydrate diet and is metabolized into normal body constituents.
Single doses of GDL in excess of 20 grams exert a laxative effect in
man.
EVALUATION
Estimate of acceptable daily intake for man
ADI "not specified". The fact that high doses of GDL exert a
laxative effect in man should be taken into account when considering
its level of use.
REFERENCES
Chenoweth, M.B., Civin, H., Salzman, C., Cohn., & Gold H. (1941).
Further studies on the behaviour of gluconic acid and ammonium
gluconate in animals and man. J. Lab. Clin. Med.,
26, 1574-1582.
Eyles, R. & Lewis, H.B. (1943). The utilization of
d-glucono-delta-lactone by the organism of the young white rat.
J. Nutr., 26, 309-317.
FDRL, (1974). Teratologic evaluation of FDA 71-72 (glucono
delta-lactone). Prepared under Contract No. FDA 71-260 by Food
and Drug Research Laboratories, Inc. 58 pp. Available from:
National Technical Information Service, Springfield, VA, USA;
No. PB-223,830.
Gajatto, S. (1939). Richerche farmacologiche sul gluconato di sodio,
Arch. di Farmacol. sper., 68, 1-13.
Gold, H. & Civin, H. (1939). Gluconic acid as a urinary acidifying
agent in man. J. Lab. Clin. Chem., 24, 1139-114b.
Harper, K.H. & Gaunt, I.F. (1962). Unpublished report from Huntingdon
Research Center
Levvy, G.A., Hay, A.J., & Conchie, J. (1964). Inhibition of
glycosidases by aldonolactones of corresponding configuration.
4. Inhibitors of mannosidase and glucosidase. Biochem. J.,
91, 378-384.
Litton Bionetics, Inc. (1974). Mutagenic evaluation of compound 71-72
glucono delta-lactone. 37 pp. Available from: National Technical
Information Service, Spingfield, VA, USA; No. PB-245,498.
Palmer, T.N. (1971). The maltase, glucoamylase and transglucosylase
activities of acid delta-glucosidase from rabbit muscle.
Biochem. J., 124, 713-724.
Roberts, B.D., Bailey, G.D., Buess, C.M., & Carper, W.R. (1978).
Purification and characterization of hepatic porcine
gluconolactonase. Biochem. Biophys. Res. Commun., 84, 322-327.
Stetten, M.R. & Stetten, D. Jr. (1950). The metabolism of gluconic
acid. J. Biol. Chem., 187, 241-252.
Tharandt, L., Hubner, W., & Holman, S. (1979). Untersuchugen uber die
Verwertung von D-Gluconat und D-Glucono-delta-lacton im
Stoffwechsel der normalen und alloxandiabetischen Ratte.
J. Clin. Chem. Clin. Biochem., 17, 237-267.
Tu, J.I., Jacobson, G.R., & Graves, D.J. (1971). Isotopic effects and
inhibition of polysaccharide phosphorylase by 1,5-glucono-
lactone. Relationship to the catalytic mechanism. Biochemistry,
10, 1229-1236.
Van Logten, M.J., den Tonkelaar, E.M., Kroes, R., Berkvens, J.M., &
van Esch, G.J. (1972). Long-term experiment with canned meat
treated with sodium nitrite and glucono-delta-lactone in rats.
Food Cosmet. Toxicol., 10, 475-488.